I can see what you mean .. also can agree with much of that perspective.
OTOH, I do not think any of us gets to redefine terms like perfect/done/solved. Talking about your distortion example, there is only one perfect/done/solved in engineering terms: zero distortion. And not only at one frequency but at "all" of them.
And that's only "perfect in engineering terms" because many ears/brains/people may not agree at all. But let's not even talk about that
As about "inaudible", I do not see that in the same category as perfect/done/solved. That threshhold is not even clearly defined. And it's a can of worms cause anyone can re-define "inaudible for me".
It's fine for someone to say "amps are a solved issues for me". About any device. But to proclaim that "amplification was solved, move along" is quite different. IMO, that's a case of Pauli's
not-even-wrong.
Anyway .. mine is not exactly a popular oppinion and it does not have to be .. and not sure what is the topic of this thread but we are surely off